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[flang] Updated the description of `evaluate::Expr` types 

Original-commit: flang-compiler/f18@75adddd504
Reviewed-on: https://github.com/flang-compiler/f18/pull/979
This commit is contained in:
Pete Steinfeld 2020-02-03 10:31:30 -08:00
parent 9d2d587763
commit b9e9b6f84d
1 changed files with 11 additions and 12 deletions
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23
flang/documentation/ImplementingASemanticCheck.md
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@ -214,22 +214,21 @@ existing framework used in DO construct semantic checking that traversed an
be able to use a similar framework to traverse an `evaluate::Expr` node to
find all of the `evaluate::ActualArgument` nodes.
Note that there are two distinct data types in the compiler called `Expr`. One
is in the `parser` namespace. `parser::Expr` is defined in the file
Note that the compiler has multiple types called `Expr`. One is in the
`parser` namespace. `parser::Expr` is defined in the file
`include/flang/parser/parse-tree.h`. It represents a parsed expression that
maps directly to the source code and has fields that specify any operators in
the expression, the operands, and the source position of the expression.
The second `Expr` type is in the `evaluate` namespace. The `evaluate`
namespace contains many types associated with semantic checking of expressions.
`evaluate::Expr` is defined in the file `include/flang/evaluate/expression.h`.
It represents an expression after it has undergone semantic checking and
contains information that is only available after semantic analysis. This
information includes the Fortran type of the expression, whether it's a
reference to a function, whether it's an actual argument, etc. After an
expression has undergone semantic analysis, the field `typedExpr` in the
`parser::Expr` node is filled in with a pointer to the analyzed expression in
`evaluate::Expr`.
Additionally, in the namespace `evaluate`, there are `evaluate::Expr<T>`
template classes defined in the file `include/flang/evaluate/expression.h`.
These are parameterized over the various types of Fortran and constitute a
suite of strongly-typed representations of valid Fortran expressions of type
`T` that have been fully elaborated with conversion operations and subjected to
constant folding. After an expression has undergone semantic analysis, the
field `typedExpr` in the `parser::Expr` node is filled in with a pointer that
owns an instance of `evaluate::Expr<SomeType>`, the most general representation
of an analyzed expression.
All of the declarations associated with both FUNCTION and SUBROUTINE calls are
in `include/flang/evaluate/call.h`. An `evaluate::FunctionRef` inherits from